Ultrasonic imaging equipments have been widely used, and they conventionally comprise an ultrasonic probe for transducing an ultrasonic wave to an electric signal, a processing unit for processing the electric signal to an image and a display unit for displaying the image. The ultrasonic probe plays an important role in obtaining high-resolution image, and it is required to have a high electromechanical coupling coefficient, as well as good ultrasonic wave pulse and focusing characteristics of ultrasonic beam.
An ultrasonic probe typically comprises an ultrasonic transmitting/receiving element consisting essentially of a piezoelectric element having a pair of electrodes, and as the piezoelectric element, lead zirconate titanate-based ceramics (PZT) was previously employed, but recently, a lead zirconia niobate-lead titanate (Pb(Zn1/3Nb2/3)O3-PbTiO3; “PZN-PT”)- or lead magnesium niobate-lead titanate (Pb(Mg1/3Nb2/3)O3-PbTiO3; “PMN-PT”)-based piezoelectric single crystals have become favored because of their better properties. However, PZN-PT and PMN-PT have the disadvantage of poor thermal stability due to a low phase transition temperature. For example, while PZT has a phase transition temperature range of about 200 to 385° C., 0.67 PMN-0.33 PT exhibits the phase transition phenomena at about 150° C. If a piezoelectric element is subjected to a temperature higher than the phase transition temperature, it will become depolarized, and thus, the preparing process of an ultrasonic probe using such piezoelectric elements should not involve a high-temperature step.
Accordingly, the electrical connection in an ultrasonic probe has been often achieved by using an epoxy paste which does not require a high temperature, rather than by soldering. However, the insertion of an epoxy paste layer tends to degrade the performance of the ultrasonic probe, and the connection of a flexible printed circuit board (FPCB) thereto requires an elaborate fabrication procedure. Although a silver epoxy paste having a better conductivity than a non-silver epoxy paste has been used in an attempt to reduce the thickness of the epoxy paste layer, the above-mentioned low performance problem remains unresolved.